In the formation of reinforced concrete pipes in a vertical position, in order to obtain the required density of the mix within the form to provide the necessary strength to the pipe and to eliminate voids, it was found in the prior art that it was desirable to use a vibration form of compacting or settling the mix as it was put into the form.
"No slump" concrete is always used in the formation of reinforced concrete pipe in which the jacket, or, core and jacket are removed immediately after the pipe has been formed. The no slump concrete is placed in the form and then packed and densified by various methods.
One method is to vibrate the "no slump"concrete which turns it into a fluid mix causing the mix to settle and density. When the vibration ceases, the fluid mix reverts back to a firm, dense, stable mix so that the jacket and core forms can be removed immediately without causing the newly made pipe to collapse.
All vibrating type molds cause the finer particles of the fluid mix, i.e., a mixture of water, cement and fine sand, hereinafter referred to as "slurry" to seek any crevice or open space in the forms from whence it could leak out. Previous vibrating machines, such as those described in U.S. Pat. No. 3,119,165 and 3,273,216, had a leakage at the junction of the jacket and bottom pallet and/or at the junction of the bottom pallet and the core or even in both places. In those machines known in the prior art, which were composed of two and three-piece jackets and/or cores, there was an additional leakage at the horizontal joints of such jackets or vertical joints in those instance of jackets which were hinged.
The loss of slurry from any mold is serious not only because of the weakening of the pipe and the change in the appearance of the pipe, but also because a grinding compound is really formed from the slurry, and when it falls or splatters on the moving parts of the apparatus, it causes unnecessary wear and maintenance, is wasteful and creates an unnecessary cleanup problem.
In those machines such as described in U.S. Pat. Nos. 2,966,716, 3,047,929 and 3,334,390, which used various types of rubber or elastic seals, the slurry provided a coating on the core and jacket that had an abrasive action which formed almost a grinding compound. The movement of the jacket and core caused wear on the seals, and it was necessary to continually readjust the seals or to replace them as the grinding became severe.
In other types of known machines, the problem of slurry was recognized, and the seals could be made more liquid-tight with respect to the core and jacket. However, when the sealing relationship was such as to make the mold liquid-tight, then the vibration was either greatly dampened as a result of the deadening effect of the seals, or an unusual amount of vibration was required in order to offset the damping effect.
The problems as set forth above were overcome in Applicant's U.S. Pat. No. 3,584,356 which is incorporated in its entirety herein by reference thereto.
As much improvement as Applicant'U.S. Pat. No. 3,584,356 contributed to the art, the apparatus and method was not always completely satisfactory. Under ordinary and practical working conditions, it is necessary that there be extremely close tolerances in the vertical positioning of the outer jacket and the inner core in relation to the fixed position of the bottom pallet. There was also a requirement for close tolerances in the horizontal relationship between the horizontal flanges of the bottom pallet and the outer jacket and the core. If these tolerances were exceeded it could result in one of more of the following problems: (a) leakage of the cement slurry; (b) variations in the wall thickness of the pipe at the groove or female end thereof; (c) a grinding action could develop between the inner edge of the bottom pallet and the bottom walls of the core which caused extreme wear on the core; (d) an excessive pressure was sometimes imposed upon the seals which dampened vibration. These tolerances were on the order of 1/16th inch plus or minus from the norm in both the vertical and horizontal positions.
These seals as set forth in the Applicant's prior patent, while superior to what was previously known in the art, occasionally resulted, and too often from a commercial standpoint, in the making of a small ridges or vertical flanges on the female ends of the pipe at both the interior and exterior wall surfaces. This, of course, wasted a small amount of material but, perhaps more importantly required additional labor and time in order to remove them. If these ridges were not removed, the outer ridge would concentrate pressure on the outer edge of the groove as the pipe were stacked in horizontal layers in the storage yard or being hauled to the job site, causing a portion of the groove to break off.
These ridges were fundamentally the result of the form of the elastic sealing means used in the Applicant's prior patent. The outer jacket carried a annular elastic ring in the lower end of the outer jacket. This elastic ring was generally of rectangular cross-section, and the lower surface of the ring was in contact with the upper surface of the lower, outwardly extending flange of the bottom pallet. If the outer jacket were not set down completely on the lower flange of the bottom pallet, a space could be formed between the lower edge of the outer jacket adjacent the elastic seal and the upper surface of the lower flange of the bottom pallet flange. The sealing means between the bottom pallet and the inner core was generally an additional annular ring of elastic material which generally had a circular cross-section. This ring was carried at the top of a saddle which supported and guided the positioning of the bottom pallet which had an interior opening to accommodate the insertion of the inner core. The elastic seal made contact with the under surface of the upper, inwardly extending flange of the bottom pallet and with the outer wall surface of the inner core when the latter was positioned within the bottom pallet. Practical necessity required that there be a minimum tolerance of approximately 1/16th of an inch between the edge of the opening in the inner pallet and the outer wall of the inner core when it was inserted within the pallet opening.
In order to overcome the difficulties imposed by the elastic seals of Applicant's prior patent, which did prevent the leakage of the slurry, there was developed the use of expansible elastic seals between the bottom wall of the outer jacket and the outwardly extending, lower flange of the bottom pallet and between the outer wall of the inner core and the edge of the interiorly extending upper flange of the bottom pallet.
The Applicant is aware of the following prior art relating to the use of resilient membranes which are caused to function by the use of pressurized fluid in the formation of concrete pipes: U.S. Pat. Nos. 3,323,188; 3,107,158; 2,937,429; 2,052,818 and 3,548,466. In all these prior patents, the flexible membrane extends the full length of the form and its use appears to be principally that of compacting the material within the forms in order to increase the density of the pipe forming material. It is noted that in general the flexible membrane is employed against only the inner wall of the pipe being formed.
The present improvement in the sealing of the lower ends of the outer jacket and the inner core and the bottom pallet provides a more practical and working tolerance of up to 1/2 inch, plus or minus from the norm, both in the vertical positioning of the jacket and core with respect to the bottom pallet as well as the horizontal relationship between the jacket and the core and the respective outer and inner flanges of the bottom pallet. Further as the improved sealing means are subjected to pressure and move toward the respective flanges of the bottom pallet, they position the bottom pallet concentrically relative to the jacket and the inner core so that a uniform thickness of pipe is maintained, particularly with reference to the female end which is formed at this point in the apparatus. The application of positive pressure to the improved seals causes them to grip the vertical edges of the lower and upper flanges of the bottom pallet to form a liquid-tight mold which to all intents and purposes is unitary at this portion of the mold, thus causing the outer jacket pallet and inner core to vibrate in unison with no appreciable damping effect. As a result, there is no longer any abrasive action as a result of relative movement between the flanges of the bottom pallet and the outer jacket and inner core. The location of the improved seals as well as their form eliminates any downward pressure on the flanges of the bottom pallet. The use of the improved seals forms a slight taper on both the outer and inner surface of the female end of the pipe and eliminates the possibility of the production of the undesirable ridges or flanges which have been discussed above. The use of the improved sealing means also results in a smaller bottom pallet with respect to the upper and lower flanges and enables the bottom pallet to be lighter in weight and less expensive to manufacture and easier to be positioned by hand. Additionally, after the pipe has been formed, the positive pressure is released from the seals whose elastic nature causes them to tend to return to a position where they are then free of contact with the edges of the lower and upper flanges of the bottom pallet. However, the additional application of negative pressure at the prescribed times makes the stripping of the inner core and outer jacket from the green pipe easier as well as facilitating other related operations, and thus substantially no danger of any damage to the male end of the newly formed green pipe exists.